1. Field of the Invention
The present invention relates to a projection type color image display unit which composes three images transmitted through three optical shutters corresponding to three primary colors to obtain a color image.
2. Description of the Related Art
The display unit is roughly classified into a direct type and a projection type, and in case of a large screen display, the projection type is superior to the direct type. There are a variety of the projection type display units one of which is a system using the optical shutter where devices are relatively compactly received therein. The optical shutter has an image display capability, and normally includes pixels in a matrix form. A display unit having a circuit structure of an active matrix type in which a switching element is disposed at each pixel is excellent in contrast. However, a passive matrix type display unit (a simple matrix type) is also used. Further, to shutter a light, a method in which liquid crystal material is used, and the light is shuttered by a voltage or current which is applied to the liquid crystal is simple. It is needless to say that other methods have also been proposed.
Displaying a color image is normally conducted by separating the color image into three color components and composing separated colors. Therefore, three optical shutters are required. The conventional projection type color image display unit is designed as shown in FIGS. 2A and 2B.
In the display unit shown in FIG. 2A, three white lights that have passed through optical systems 2 to 4 from one light source 1 are inputted to optical shutters 8 to 10 through color filters 5 to 7. In other words, those three color filters are red, blue and green, respectively, and the optical shutters corresponding to the respective color filters display images corresponding to the respective primary colors.
Lights that have passed through the optical shutters are converged into one light through optical systems 11 to 13 to produce a color image. This color image is projected onto a screen (FIG. 2A).
In this system, since ⅔ of the incident lights are absorbed by the color filters at the minimum, the light from the light source is not sufficiently utilized with the result that the image becomes dark. In order to solve this problem, a dichroic mirror is employed, and an example thereof is shown in FIG. 2B. U.S. Pat. No. 5,337,171 discloses such a projector, the content of which is incorporated herein by reference.
First, of a white light inputted to a dichroic mirror 14 from a light source 1, lights other than a red light (lights shorter in wavelength than a red light) are reflected, and only the red light is inputted to an optical shutter 10. The remaining lights are inputted to a second dichroic mirror 15. In this example, lights other than a green light (lights shorter in wavelength than a green light), that is, a blue light is reflected and then inputted to an optical shutter 9. A light which are linearly propagated through the second dichroic mirror 15 is green, which is inputted to an optical shutter 8 through a total reflection mirror 16. The lights that have passed through the respective optical shutters are converged into one light through optical systems 11 and 12 to produce a color image. This color image is projected onto a screen (FIG. 2B).
In this system, since no light is absorbed by the color filters, the light can be efficiently utilized. In order to enhance the efficiency, a light from the light source may be an intense light consisting of the spectra of three primary colors. With this, the transmission and reflection of a light at the dichroic mirror are efficiently conducted.
Also, there has been proposed a method in which a red laser 21, a green laser 22 and a blue laser 23 are employed as light sources, and lights which are expanded by beam expanders 24 to 26 are made input to optical shutters 27 to 29, as shown in FIG. 3.
A block diagram of a picture image circuit in the projection type display unit of this type is shown in FIG. 4. A video signal is information of three primary colors which are formed on a carrier wave through the AM-FM composite modulation system. The signal is separated into three primary color signals through demodulation. The demodulation operation is conducted by a xe2x80x9ccolor separationxe2x80x9d circuit. At this stage, the respective primary color signals are analog signals, but they are digitalized into digital signals by a subsequent digitalizing circuit (an analog-to-digital converter, an A/D circuit). Then, the respective primary color signals are transmitted to three optical shutters to be subjected to a xcex3-correction at the circuits provided on the respective optical light shutters. Thereafter, the digital signals are converted into analog signals by a subsequent digital-to-analog circuit (a digital-to-analog converter, a D/A circuit), and then inputted to a display unit (an optical shutter).
The color image display unit with the above structure requires a chip having a color separation circuit and an A/D circuit in addition to those three optical shutters. In other words, at least four parts for constituting the circuit are required at the minimum.
Also, there arises such a problem that in the color separation circuit or the A/D circuit, when a noise is intermingled therein, it cannot be finally removed therefrom.
The present invention has been made in view of the above problem, and therefore an object of the present invention is to provide a projection type color image display unit which is capable of reducing the number of parts to three at the minimum and also reducing a noise.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a projection type color image display unit, which comprises:
first to third substrates each having an optical shutter;
at least one color separation circuit in each of said first to third substrates;
at least one digitalizing circuit in each of said first to third substrates; and
at least one comparing circuit (comparator) for comparing three signals with each other in each of said substrates;
wherein a signal corresponding to red which is outputted from said digitalizing circuit in each of said first to third substrates is inputted to said comparator of said third substrate;
wherein a signal corresponding to green which is outputted from said xcex3-correction circuit in each of said first, second and third substrates is inputted to said comparator of said second substrate; and
wherein a signal corresponding to blue which is outputted from said xcex3-correction circuit in each of said first, second and third substrates is inputted to said comparator of said first substrate.
In order to achieve the above object, according to a second aspect of the present invention, there is provided a projection type color image display unit, which comprises:
first to third substrates each having an optical shutter;
at least one color separation circuit in each of said first to third substrates;
at least one digitalizing circuit in each of said first to third substrates;
at least one xcex3-correction circuit in each of said first to third substrates; and
at least one comparing circuit (comparator) for comparing three signals with each other in each of said substrates;
wherein a signal corresponding to red which is outputted from said xcex3-correction circuit in each of said first to third substrates is inputted to said comparator of said third substrate;
wherein a signal corresponding to green which is outputted from said xcex3-correction circuit in each of said first to third substrates is inputted to said comparator of said second substrate; and
wherein a signal corresponding to blue which is outputted from said xcex3-correction circuit in each of said first to third substrates is inputted to said comparator of said first substrate.
In order to achieve the above object, according to a third aspect of the present invention, there is provided a projection type color image display unit, which comprises:
first to third substrates each having an optical shutter;
at least one color separation circuit in each of said first to third substrates;
at least one digitalizing circuit in each of said first to third substrates;
at least one time-axis correction circuit in each of said first to third substrates; and
at least one comparing circuit (comparator) for comparing three signals with each other in each of said substrates;
wherein a signal corresponding to red which is outputted from said time-axis correction circuit in each of said first to third substrates is inputted to said comparator of said third substrate;
wherein a signal corresponding to green which is outputted from said time-axis correction circuit in each of said first to third substrates is inputted to said comparator of said second substrate; and
wherein a signal corresponding to blue which is outputted from said time-axis correction circuit in each of said first to third substrates is inputted to said comparator of said first substrate.
The projection type color image display unit according to the present invention is useful in case of applying to a structure in which an active matrix circuit, a peripheral drive circuit, a color separation circuit, an A/D circuit, a comparator circuit, a xcex3-correction circuit, a D/A circuit and so on are integrated on one substrate using thin-film transistors.
This is because, in the case where the respective circuits are integrated on the same substrate using the thin-film transistors, there are many cases in which the performance of the circuits is dispersed in the respective substrates, but, such dispersion can be suppressed with an employment of the above structure according to the present invention.
In other words, the signals processed in other substrates are compared and employed, thereby being capable of reducing the dispersion of the characteristics of the respective substrates.
In the present invention, various types of the comparators are proposed. For example, it may be a circuit for operating a mean value of three signals. Alternatively, it may be a circuit for outputting signals having two or more identical values among three signals, a circuit for operating a mean value of two values which are the closest among three signals, or the combination thereof.
In any cases, it may be employed a structure through which influence caused by the abnormal value can be reduced as much as possible when there is an abnormal value in three signals. For example, in the case of applying a mean value of three signals in the comparator, the S/N ratio (signal/noise ratio) becomes {square root over (3)} times.
As is apparent from the above structures, in the present invention, the circuit can be structured by only three optical shutters, and the number of parts can thus be reduced to three at the maximum. Also, since the abnormal value can be reduced by the comparators, the noise or the operation failure is reduced.
Further according to a fourth aspect of the present invention, there is provided a projection type color display unit, which comprises:
N-substrates (N=3, 4, 5 . . . ) each having an optical shutter;
at least one color separation circuit in each of said substrates; and
at least one digitalizing circuit in each of said substrates;
wherein a common digital processing is conducted on all of said substrates; and
wherein a digitalized signal which is processed in one of said N-substrates is inputted to another one of said N-substrates.
A specific example of the above structure is shown in FIG. 1. In the structure shown in FIG. 1, A/D circuits which are one kind of the digital circuits are commonly arranged in all of three substrates (N=3) in such a manner that a common processing is conducted in all the A/D circuits.
Also, a signal which has been processed in one substrate is employed in all other substrates.